Method for identifying surface conditions of a moving medium

ABSTRACT

A method and apparatus for mapping the character and location of medium conditions for a planar surface. Energy is supplied to a head in close proximity to the planar surface to thereby raise the temperature of the object. The head is moved with respect to the planar surface while keeping the distance from the planar surface substantially constant. An increase, decrease or a rapid variation containing positive and negative temperature excursions is distinguished by electronic means. These variations are used to categorize disturbances or contact with the medium, and the location and type of condition is recorded in hard copy or by computer acquisition for later consideration in the file manufacture process. Additionally, magnetic and thermal information may be combined to provide an even more complete description of the nature of the condition, since the magnetic and thermal signals are descriptive of different physical phenomenon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of United States patent applicationentitled SYSTEM FOR IDENTIFYING SURFACE CONDITIONS OF A MOVING MEDIUM,filed May 6, 1996, Ser. No. 08/643,193, which itself is aContinuation-In-Part of United States patent application entitled METHODAND APPARATUS FOR THERMAL PROXIMITY IMAGING, filed Apr. 30, 1993, Ser.No. 08/056,164, now U.S. Pat. No. 5,527,110, issued Jun. 18, 1996.

U.S. Pat. No. 5,527,110 is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

This invention relates generally to a method and an apparatus for thecategorization of medium conditions on a surface, by detecting thepresence and nature of these conditions using thermal conduction. Morespecifically, the invention relates to a method and apparatus foranalyzing and categorizing medium conditions on the surface of arotating disk in a direct access storage device, such as a magnetic diskdrive.

BACKGROUND OF THE INVENTION

In data processing systems, magnetic disk drives are often used asdirect access storage devices. In such devices, read-write heads areused to write data on, or read data from, an adjacently rotating hard orflexible disk. To prevent damage to either the disk or the read-writehead, it has been recognized for a long time that the surface of thedisk should be very flat and free of any bumps or the like which mightbe contacted by the read-write head. Also, the read-write heads havebeen designed so that they will fly over the surface of the rotatingdisk at a very small, though theoretically constant, distance above thedisk, the separation between the read-write head and the disk beingmaintained by a film of air. During its flight, the head undergoescontinuous vibration, pitch and roll as the topography of the diskchanges beneath the head. If the quality of the disk or the read-writehead is poor, occasional rubbing or sharp contact may occur between thedisk and the read-write head, leading to damage to the head or to thedisk, and possibly the loss of valuable data.

Various attempts have been made to provide increased assurance that suchundesirable contact between a read-write head and a recording disk doesnot occur. Rigid manufacturing and quality assurance specifications forboth the recording disk and the read-write head have been instituted.

Disk inspection for various types of defects, including magnetic,optical and topographic (i.e., delamination, voids and inclusions,generally known as asperities), is of critical importance for theincreasingly stringent production requirements facing a manufacturertoday as smaller drives store more data. Many methods of inspection tofind defects are in use, and many more have been proposed. These includeoptical techniques (fiber interferometry, bulk optic shearinterferometry, microISA), magnetic readout (simply screening, HRF,etc.,) and mechanical testing (the so-called PZT glide test, describedbelow). Each of these techniques may play a role in achieving the goalof the virtually defect free production of magnetic disks. However, witha tightening market and more exacting technical requirements as headsfly lower and faster, less expensive and more accurate inspectionschemes become desirable.

The PZT glide test is disclosed in U.S. Pat. No. 4,532,802 toYeack-Scranton et al. A read-write head is provided with a plurality ofpiezo-electric transducers which produce signals related to its movementas it flies over an adjacently rotating recording disk. By filteringthese signals to determine their spectral components in low, medium andhigh ranges, hard contacts between the head and disk, disk wear orroughness, and head movement can be determined. While quite satisfactoryin many aspects, this technique depends on contact between theread-write head and the disk, and as a result the heads wear out andcostly replacement is required. In addition, resolution in the radialdirection is limited by the geometry of the head to about 2 mm in theradial direction.

U.S. Pat. No. 4,747,698 to Wickramasinghe et al. is directed to aScanning Thermal Profiler. A fine scanning tip is heated to a steadystate temperature at a location remote from the structure to beinvestigated. Thereupon, the scanning tip is moved to a positionproximate to, but spaced from the structure. At the proximate position,the temperature variation from the steady state temperature is detected.The scanning tip is scanned across the surface structure with theaforesaid temperature variation maintained constant. Piezo electricdrivers move the scanning tip both transversely of, and parallel to, thesurface structure. Feedback control assures the proper transversepositioning of the scanning tip and voltages thereby generated replicatethe surface structure to be investigated. While this approach providesexcellent depth resolution, it requires the use of an expensive scanningtip. It also has, in common with the approach illustrated in U.S. Pat.No. 4,532,802 discussed above, the disadvantage that it cannot readilybe utilized on an assembled disk drive.

What is needed is a method and apparatus for the detection of surfaceconditions on an otherwise smooth surface. The method and apparatusshould provide for the subsequent categorization of the conditions intoone of a plurality of possible types. Further, the method and apparatusshould be useable in assembled disk drives, and provide the requisitefunction at a lower cost than the prior art systems.

SUMMARY OF THE INVENTION

The present invention, in one aspect, is a method for identifyingsurface disturbances on a medium moving relative to a head, includingmonitoring a thermal environment over the moving medium with the headand processing the monitored thermal environment. By processing themonitored thermal environment, a type of a surface disturbanceencountered on the moving medium is identified. Further, an interactionbetween the head and the medium is identified using the monitoredthermal environment. The monitoring may include providing a signalindicative of the thermal environment, and the type of surfacedisturbances is identified by determining whether the signal falls belowa first level or whether the signal rises above a second level. Theinteraction is identified by determining whether, within a predeterminedtime period, the signal oscillates between the first and second levels.

The first type of surface disturbance may be a protrusion typedisturbance, which causes a temperature of the monitored thermalenvironment to decrease, and the second type of surface disturbance maybe a recess type disturbance, which causes the temperature of themonitored thermal environment to increase.

In another aspect, the method includes monitoring a magnetic environmenton the moving medium, and processing the monitored magnetic environment.By processing the monitored magnetic environment, a magnetic defectencountered on the moving medium can be detected. Thus, the presentinvention combines disturbance detection and identification using boththe magnetic and thermal environments of the moving medium.

In another aspect, the present invention is a system for identifyingsurface conditions of a medium moving relative to a head. The systemincludes an input node for receiving an input signal representative of athermal environment over the medium, a first processing path coupled tothe input node for determining whether the input signal receivedtherefrom meets a first criteria (e.g., recess), and a second processingpath coupled to the input node for determining whether the input signalreceived therefrom meets a second criteria (e.g., protrusion). Thesystem may include a circuit for determining whether the input signalmeets a third criteria, the third criteria corresponding to anoscillating signal indicative of an interaction between the head and themedium. The system includes a comparator, pulse generator, referencesignal, and AND gate for the first and second processing paths, in oneembodiment.

The system may further include another input for receiving another inputsignal representative of a magnetic environment on the medium. Amagnetic environment processing path may be provided for processing themagnetic input signal and detecting magnetic defects therefrom.

The method and system of the present invention overcome the shortcomingsof the prior art in that medium conditions can be sensed and categorizedinto a plurality of types. Further, the addition of magnetic defectsensing allows categorization and qualification of the defect types, andcauses thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged view of a read-write head flying over a rotatingdisk having disturbances thereon;

FIG. 2 is a diagram, partially schematic and partially in block, of athermal proximity imaging apparatus;

FIG. 3a is a plot of the amplitude of the signal from a protrusion-typesurface disturbance versus spatial position;

FIG. 3b is a plot of the amplitude of the signal from a recess-typesurface disturbance versus spatial position;

FIG. 3c is a plot of the amplitude of the signal resulting from contactbetween the sensor head and the medium;

FIG. 4 is a schematic diagram of an exemplary apparatus according to thepresent invention, which provides the discrimination of three types ofmedium conditions in an automated fashion; and

FIG. 5 is a schematic diagram of an exemplary apparatus according to thepresent invention, which provides both thermal and magnetic sensing ofsurface conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a head (10, 16) mounted on an actuator 11, used todetect medium conditions is depicted. These conditions may includesurface disturbances (e.g., protrusions or recesses, which are generalterms used herein to refer to disturbances sometimes known asasperities, pits, bumps, defects, particles, etc.) and/or magneticdisturbances and/or contact with the head. The geometry of the slider 10with relation to the disk 12 and a recess 13 and a protrusion 14 isshown.

As is well known in the art, disk 12 rotates on a spindle 15, driven bya motor 18. (Any type of relative motion between the head and the mediumis referred to herein as the medium moving relative to the head. Thisnaturally includes a moving medium and fixed heads, spinning disks,moving tapes, or can be a moving head and fixed medium, or anycombination thereof.) An encoder 17 provides data on the relativerotational orientation of disk 12 with respect to slider 10. (The term"head" when used herein, broadly connotes any device used in associationwith a medium, including, but not limited to, the slider, MR element orstripe, or any thermal or magnetic sensing device, or any combinationthereof, such as that depicted in FIG. 1.)

Slider 10 has an air bearing surface facing disk 12. The relative motionof the air bearing surface of slider 10 and the planar surface of disk12 maintains the distance between the slider 10 and disk 12substantially constant. The air bearing surface of slider 10 is designedto provide a constant fly height (for a given rotational disk speed) ofslider 10 above the surface of disk 12. The head temperature is elevatedusing Joule heating of the exemplary MR element or stripe 16. As thehead passes over the disk it is cooled in part by conduction. If aparticle causes the gap spacing to temporarily vary, the temperaturewill cool and can be sensed as a momentary spike in the head readoutsignal due to its non-zero temperature coefficient of resistance. Theamplitude of the spike is proportional to the temperature differentialmaintained in the MR head versus the disk surface and to the thermalproperties of the asperity, and depends roughly as 1/d where d is thehead-disk spacing (as opposed to the roughly average fly height).

Even in standard operation, the MR stripe 16 can be expected to runquite hot, since typical bias currents are in the range of 10-20 mA,with head resistances of a few tens of ohms. Thus, in a head/sliderweighing no more than a gram, tens of milliwatts in Joule heatingoccurs. The temperature rise can be expected to be significant, and infact proportional to the square of the current. The temperature risewill be determined by this heat flow, balanced by convective and/orconductive losses into the atmosphere and the disk. Further heating canbe supplied with a resistor, and in fact may be desirable in order tobias the magnetic sensitivity to near zero. Typically, MR elements havea thermal sensitivity of resistance of 3×10⁻³ /°K. By avoidingsubstantial bias at the frequency used to measure the resistance of theelement, magnetic contributions can be nearly eliminated.

Particle size can be estimated from the strength of the thermal signal.The effectiveness of cooling depends on both the width and height of theprotrusion (or recess), and during the scan past the disturbance a fixedamount of heat energy will flow to the disk surface.

Use of existing MR head technology has several advantages. First, noadditional development need be done, and implementation in a test standcan be achieved with little extra cost. Second, a large knowledge baseexists about MR head properties, so that complete understanding ofthermal response versus magnetic properties can be had at small addedeffort. Third, no modification of the head is required, so thatsignificant costs in replacement heads is avoided (as exists with thePZT glide tester described in U.S. Pat. No. 4,532,802). Fourth,topographic screens and magnetic evaluation can be performedsimultaneously, which is important as a time saver, and for providingnew information correlating the two properties. Fifth, this techniquecan provide higher resolution and less ambiguous information aboutdisturbances than piezo-based methods or magnetic methods alone.

Finally, the technique can be used to evaluate disks in assembledhead-disk assemblies of disk drives.

The above-referenced U.S. patent application Ser. No. 08/056,164, nowU.S. Pat. No. 5,527,110 to Abraham et al., is directed to the concept ofThermal Proximity Imaging ("TPI"), which consists of a method formapping the character and location of small surface variations on aplanar surface. In practice, TPI employs a heated resistive sensormoving in close proximity to the surface under inspection. Thetemperature of the head, and therefore the resistance of the sensor, aredependent on the spacing between the sensor and the inspected surface.The energy supply required to heat the sensor above ambient temperaturemay be thermal energy or optical energy but preferably is electricalenergy which heats a resistive element. Preferably, the element is themagnetoresistive head of a disk drive assembly. The change intemperature is detected by monitoring the resistance of themagnetoresistive sensor of the head. The energy may be supplied inpulses to obtain higher peak temperatures while avoiding mechanicaldistortion of the object. It is preferred that the object be positionedwith respect to the surface so that when that relative motion betweenthe surface and the object occurs, the object does not contact thesurface. As discussed further below, the present invention provides amethod and apparatus to perform a detailed interpretation of the thermalenvironment or signature received from such a system.

Referring to FIG. 2, an exemplary TPI system for obtaining andevaluating data from slider 10 is illustrated. A pre-amplifier circuit20 provides a bias current to the magnetic stripe 16 of slider 10 (FIG.1). A potentiometer 22 connected to a voltage source 24 at one end andground at the other end permits adjustments of the bias current. Theslider of the potentiometer is connected to one side of magnetic stripe16 (or, alternatively, to an inductive coil) of slider 10. The otherside of stripe 16 is connected to ground, as is the side of voltagesource 24 not connected to potentiometer 22.

Voltage source 24 may supply direct current, alternating current, orpulses having one polarity or alternating polarities. For the highestsensitivity, and therefore the best resolution of height of aprotrusion, pulses are preferred. Pulsed operation permits the highestpeak temperatures without overheating the slider 10 so as to causemechanical distortion thereof.

Capacitor 26 and resistor 28 form a high pass filter which passessignals from the slider 10 to the non-inverting input of an operationalamplifier 30.

Resistor 32 connected from the output of the operational amplifier tothe inverting input and resistor 34 connected from the inverting inputto ground determine the gain of operational amplifier 30, in a mannerwell known in the art. Typically, resistors 32 and 34 are selected sothat operational amplifier 30 has a gain of 500.

Output signals from amplifier 30 are provided as Y axis inputs to afirst channel of an oscilloscope 36. The same signals are sent to a lowpass filter 38 and then to a Y axis input of a second channel ofoscilloscope 36. The signals from a protrusion on the disk are generallyin the form of a sharp spike having a 3 dB width corresponding to a timeof less than 50 microseconds, or typically less than 250 microns of disktravel. These spikes are displayed on the first channel of oscilloscope36. The magnetic data, which typically does not change amplitude asrapidly, passes through filter 38 and may be viewed on the secondchannel of the oscilloscope 36.

The signals from amplifier 30 are also supplied to a computer interface40 which includes an analog-to-digital converter, of a type well knownin the art, which converts the analog signals from operational amplifier30 to digital form, for acquisition by a computer 42.

Information concerning the rotational position of the slider 10 withrespect to the disk, provided by shaft encoder 17, which may be a pulsefor every revolution of disk 12 is used as a synchronization input tooscilloscope 36. It is also used as a so-called θ position input. It istherefore supplied to computer interface 40 for eventual use by computer42.

The position of slider 10 in the radial direction with respect to disk12 is determined by a head position sensor 43 associated with theactuator 11 for slider 10. This radial position information is alsosupplied to computer interface 40.

The information supplied to computer interface 40 provides threedimensional data where the θ and radial position data define theposition of a disturbance on the disk 12, while the information derivedfrom the output of amplifier 30 provides an indication concerning theseverity of the disturbance, with respect to height. The information isstored in a data base in computer 42, processed by suitable processingtechniques and finally displayed on a display screen 44. Alternatively,a hard copy print out is provided by a printer 46.

FIGS. 3a, 3b and 3c respectively are plots of the thermal voltageproduced across the magnetoresistive head as it passes across adisturbance corresponding to a protrusion above the disk surface, to adisturbance corresponding to a recess below the disk surface, andfinally to an interaction or contact of the head and the disk, possiblycaused by a protrusion of sufficient height. It can be seen, as thepresent inventors have discovered, that there is a qualitativedifference between what are referred to herein as these three mediumconditions, i.e., protrusions, recesses, and contact.

In FIG. 3a, a close approach of the disk surface due to the presence ofa protrusion smaller than the head-disk gap clearance causes thetemperature of MR head to adjust slightly downward during the time ofpassage of the defect past the sensor. This causes a reduction in the MRresistance due to the positive thermal coefficient of resistivity and aconcomitant negative voltage spike.

In FIG. 3b, a recess caused in this case by a delamination of themagnetic layer probably due to contamination at the plating phase ofmanufacture is imaged by thermal means. The voltage trace in this caserises, since as the recess passes under the magnetoresistive element thehead-disk gap clearance increases and the temperature rises. Since atemperature rise is associated with a MR element resistance rise, thevoltage for constant bias shows a positive spike.

Finally, in FIG. 3c, the head has passed over a protrusion rising abovethe average disk surface, with sufficient height so as to cause theslider to substantially impact (i.e., an interaction) with theprotrusion and in fact cause a deflection and subsequent vibration untilthe flight of the slider returns to a stable configuration. As before,the thermal signal reflects the gap clearance variation, and asignificant signal is observed in both positive and negative voltages asthe head fly height oscillates about its mean value.

By noting the different reaction of the thermal voltage to these threekinds of medium conditions, and in accordance with the principles of thepresent invention, it is possible to automatically categorize mediumconditions according to type.

FIG. 4 shows a schematic diagram of an exemplary apparatus for carryingout this classification according to the principles of the presentinvention. The signal input node 100 (representative of the thermalenvironment monitored by the head over the medium) is driven by thepreamplifier 20 (FIG. 2), and the input signal is fed to the positiveinput of a comparator 101 (the beginning of a first processing path),and to the negative input of another comparator 102 (the beginning of asecond processing path). The negative input of comparator 101 is set bya voltage (e.g., first reference level) determined by a variableresistor 103 which is biased between positive voltage supply and ground.

Correspondingly, the positive input of comparator 102 is set by avoltage (e.g., second reference level) determined by variable resistor104, which is biased between negative supply voltage and ground.

Comparator 101 therefore functions in a non-inverting mode and providesa constant positive voltage (e.g., an active first signal) at its outputduring the time the input signal 100 exceeds the positive voltage set byvariable resistor 103. Comparator 102 therefore functions in aninverting mode and provides a constant negative voltage (e.g., an activesecond signal) at its output during the time the input signal is morenegative than the negative voltage set by variable resistor 104.

Attached to the output of the comparators 101 and 102 are one-shottriggered gates or pulse generators 105 and 106, respectively. If thegates are triggered, a pulse appears at the outputs. Each gate 105 and106 has an associated predetermined time constant, such that if a shortpulse triggers the gate, the output pulse rises and holds for apreconditioned period of time equal to the time constant. In practice,the time constant is adjusted to be several periods of the airbearingoscillation frequency, or roughly 0.1 ms.

The outputs of one-shots 105 and 106 are combined in three logicalpaths. First, AND gate 107 combines the output from gate 105 and thelogical negative of gate 106, resulting in an output marked RECESS.Next, AND gate 108 combines the output of gate 106 and the logicalnegative of gate 105, resulting in an output marked PROTRUSION. Finally,the outputs from gates 105 and 106 are combined at AND gate 109,resulting in an output marked CONTACT.

According to the convention established in FIG. 4 wherein the pulsesoutput from the pulse generators or one-shots 105 and 106 are labeled`A` and `B` respectively, the first output signal RECESS provided by ANDgate 107 is active when only the A pulse is active (indicating a highinput signal 100), and the B pulse (applied to the inverted input) isinactive. Similarly, the second output signal PROTRUSION provided by ANDgate 108 is active when only the B pulse is active (indicating a lowinput signal 100), and the A pulse (applied to the inverted input) isinactive. Finally, the third output signal CONTACT provided by AND gate109 is active when both the A and B pulses coincide in time (indicatingan oscillation of input signal 100 between positive and negative levelsduring the predetermined pulse width window established within gates 105and 106). These three criteria (high input signal level, low inputsignal level, and oscillating input signal) are therefore automaticallysensed by the circuit of FIG. 4, and the existence of these conditionsis provided to a follow-on user via the three output signals RECESS,PROTRUSION and CONTACT.

The function of the circuit can be understood as follows.

When a non-contact protrusion type disturbance is passed under the head,a negative voltage spike is produced. By comparing the voltage spikeamplitude to a reference level set by the potentiometer 104, thecomparator 102 will change state only if the protrusion exceeds apredetermined height, as determined by suitable calibration of thethermal voltage as a function of defect height. The comparator spike isof roughly the same duration as the original thermal signal, but isconstrained to a fixed voltage value during the spike. This short spikeis fed to a one-shot trigger 106 in order to broaden the spike signal intime. This accomplishes two goals. First, detection of the event bycomputer means is easier since the sampling rate can be substantiallyreduced. Second, coincidence measurements of positive and negativevoltage spikes are made within a window, rather than precisely at thesame moment. Thus, an oscillating thermal signal will trigger AND gate109 if the predetermined time constants of gates 105 and 106 aresufficiently long.

The PROTRUSION output of gate 108 will function such that only when anegative spike and no positive spike within the time windows defined bythe one-shots 105 and 106 will a signal be observed. Similarly, theRECESS output of gate 107 will function such that only when a positivespike and no negative spike within the time windows defined by theone-shots 105 and 106 will a signal be observed.

Further discrimination as to the type of condition can be obtainedaccording to the principles of the present invention by combiningthermally derived signals from the sensor with the signals obtained fromthe readback of magnetically recorded transitions on the disk surface.The interpretation of magnetic signals to determine surface topographyis discussed in U.S. Pat. Nos. 5,130,866 and 4,777,544, both assigned tothe assignee of the present invention, and both incorporated herein byreference in their entirety. The techniques may include CMD (ClearanceModulation Detection), HRF (Harmonic Ratio Flyheight) and QRS(Quantitative Readback Signal), known to those skilled in the art.However, by combining the thermal and magnetic data according to thepresent invention, a more accurate description of topography andspecific surface defects can be provided.

As an example, consider the first case of a magnetic defect in thesurface, but no topographic surface disturbances. This happens inseveral ways: a sub-surface void in the magnetic recording film, alocalized region of altered magnetic coercivity, a buried non-magneticparticle, etc. In these cases, usually a potentially strong reduction inthe amplitude of the magnetic signal occurs. This strong change insignal therefore may or may not correspond to a disturbance in thetopography of the surface. It is important to know whether this is thecase, since a simple magnetic defect can be avoided by simply notwriting to this region, but a topographical error could crash the head.

An improved method of analyzing the defect is to obtain thermal datasimultaneously with the acquisition of magnetic data. In the case of amagnetic defect only, essentially no deviation in the thermal signalwould be observed. The classification of this condition as "magneticdefect non-topographic disturbance" is an important distinction for harddisk defect screening and can now be made pursuant to the principles ofthe present invention.

A second case may include a non-magnetic particle on top of the surface,which is small enough to not cause contact of the head. This particlewould not result in a change of the magnetic signal, while the thermalsignal would show a change in clearance height as discussed in detailabove.

A third case may include the same type of particle which now causescontact with the head. In this case, the returns from both the magneticand thermal sensors exhibit oscillation as discussed above in connectionwith FIG. 3c.

The fourth and fifth cases generally correspond to the surfacedisturbances of recesses and protrusions, assuming a magnetic coat hasbeen placed conformally thereover. In these cases, both the magnetic andthermal sensors exhibit corresponding increases or decreases.

Table 1 distinguishes these five conditions sensed with the combinationof magnetic and thermal sensors:

                  TABLE 1                                                         ______________________________________                                        Condition    Magnetic Sensor                                                                             Thermal Sensor                                     ______________________________________                                        1. Mag. defect,                                                                            Usually appears                                                                             No change in                                       no topographic                                                                                 as signal drop                                                                           clearance                                         disturbance                                                                   2. Non-mag.         No change                                                                                  Clearance                                    particle, no                              decrease                            contact                                                                       3. Non-mag.         Clearance                                                                                  Clearance                                    particle with                                                                                   oscillation                                                                                oscillation                                    contact                                                                       4. Recess with                                                                                 Clearance       Clearance                                    mag. coat             increase                                                                                  increase                                    5. Protrusion                                                                                   Clearance                                                                                    Clearance                                    with mag. coat                                                                                 decrease         decrease                                    ______________________________________                                    

Although this breakdown of conditions as determined by theinterpretation of the magnetic and thermal signals is one potentialscheme for classification, it should be recognized that a more completetreatment of all of the data, particularly using the calibrated magneticand thermal signals, would result in a more detailed description of theparticle properties, both topographic and magnetic.

FIG. 5 depicts an exemplary system 200 which combines a thermal sensingand processing path (204, 208) and a magnetic sensing and processingpath (206, 210). The sensors (204, 206) are placed on a head 202, and aprocessor 212 is provided to combine and analyze the outputs from bothpaths, in accordance with at least the 5 cases discussed above. Sensors204 and 206 could comprise the same sensor (e.g., MR) as discussed indetail above with regard to FIGS. 1 and 2. The detectors 208 and 210could be implemented according to the general principles discussed aboveregarding FIG. 4, and/or the incorporated '866 or '544 patents.

While the description of the invention set forth above has centeredprimarily on the mapping and characterization of defects, one type ofdisturbance, it is noted that the invention may also be applied to amethod and apparatus for the storage of information using intentionallyplaced disturbances. In particular, information can be encoded into thesurface of a disk in the form of protrusions, recesses, or neither.Using the thermal imaging method and apparatus described herein, theinformation can be read back and retrieved for use in, for example, adata processing and/or storage system. Further, in view of the abilityto discriminate between magnetic signals and signals resulting from thetopography of the disk, it is possible to encode some information on thedisk using magnetic techniques and other information using topographicaltechniques. Different kinds of information can be encoded in thismanner, for example, it may be preferable to encode information to bepermanently stored by topographical techniques while information whichis to be changed can be encoded by magnetic techniques.

While the invention has been particularly shown and described withrespect to a preferred embodiment thereof, it will be understood bythose skilled in the art that changes in form and details may be madetherein without departing from the scope and spirit of the invention.

What is claimed is:
 1. A method for identifying surface disturbances ona medium moving relative to a head, comprising:monitoring a thermalenvironment over the medium with said head including to obtain a signalprimarily representative of the thermal environment over the medium; andprocessing said signal primarily representative of said thermalenvironment, includingidentifying a type of a surface disturbanceencountered on the medium using said signal primary representative ofsaid thermal environment.
 2. The method of claim 1, wherein theprocessing further includes:identifying an interaction between the headand the medium using said monitored thermal environment.
 3. A method foridentifying surface disturbances on a medium moving relative to a head,comprising:monitoring a thermal environment over the medium with saidhead; processing said monitored thermal environment includingidentifying a type of a surface disturbance encountered on the mediumusing said monitored thermal environment;wherein the monitoring includesproviding a signal indicative of the thermal environment, and whereinthe identifying a type of a surface disturbance includes: determiningwhether the signal falls below a first level, the first level indicativeof a first type of surface disturbance; and determining whether thesignal rises above a second level, the second level indicative of asecond type of surface disturbance.
 4. The method of claim 3, whereinthe identifying an interaction includes:determining whether, within apredetermined time period, the signal oscillates, said oscillating beingindicative of the interaction between the head and the medium.
 5. Themethod of claim 4, wherein the first type of surface disturbancecomprises a protrusion type disturbance, which causes a temperature ofthe monitored thermal environment to decrease, and wherein the secondtype of surface disturbance is a recess type disturbance which causesthe temperature of the monitored thermal environment to increase.
 6. Amethod for identifying surface disturbances on a medium moving relativeto a head, comprising:monitoring a thermal environment over the mediumwith said head; processing said monitored thermal environment includingidentifying a type of a surface disturbance encountered on the mediumusing said monitored thermal environment;wherein the monitoring includesproviding a signal indicative of the thermal environment, and whereinthe identifying a type of surface disturbance includes: determiningwhether the signal falls below a first level, the first level indicativeof a first type of surface disturbance; and determining whether thesignal rises above a second level, the second level indicative of asecond type of surface disturbance.
 7. The method of claim 6, whereinthe first type of surface disturbance comprises a protrusion typedisturbance, which causes a temperature of the monitored thermalenvironment to decrease, and wherein the second type of surfacedisturbance is a recess type disturbance which causes the temperature ofthe monitored thermal environment to increase.
 8. The method of claim 1,wherein a magnetoresistive element is used within the head to monitorthe thermal environment.
 9. The method of claim 8, wherein themagnetoresistive element is also used to magnetically read data fromsaid medium.
 10. A method for identifying surface disturbances on amedium moving relative to a head, comprising:monitoring a thermalenvironment over the medium with said lead; processing said monitoredthermal environment including identifying a type of a surfacedisturbance encountered on the medium using said monitored thermalenvironment; monitoring a magnetic environment on the medium; andprocessing said monitored magnetic environment includingdetecting amagnetic defect encountered on the medium using said monitored magneticenvironment.
 11. The method of claim 10, wherein the type of surfacedisturbance identified is a protrusion, the method furthercomprising:determining, using the monitored magnetic and thermalenvironments, whether the protrusion is intrinsic to said medium or aparticle on said medium.
 12. A method for identifying surfacedisturbances on a medium moving relative to a head,comprising:monitoring a thermal environment over the medium with saidhead; processing said monitored thermal environment includingidentifyinga type of a surface disturbance encountered on the medium using saidmonitored thermal environment, identifying an interaction between thehead and the medium using said monitored thermal environment; monitoringa magnetic environment on the medium; and processing said monitoredmagnetic environment includingidentifying said type of surfacedisturbance encountered on the medium using said monitored magneticenvironment, and identifying said interaction between the head and themedium using said monitored magnetic environment.
 13. A method foridentifying conditions of a medium moving relative to a head,comprising:monitoring a thermal environment over the medium with saidhead using a signal primarily representative of the thermal environmentover the medium; and processing said signal primarily representative ofsaid thermal environment includingdetecting a surface disturbanceencountered on the medium using said monitored thermal environment, anddetecting an interaction between the head and the medium using saidmonitored thermal environment.
 14. A method for identifying conditionsof a medium moving relative to a head, comprising:monitoring a thermalenvironment over the medium with said head; processing said monitoredthermal environment includingdetecting a surface disturbance encounteredon the medium using said monitored thermal environment, and detecting aninteraction between the head and the medium using said monitored thermalenvironment;wherein the monitoring includes providing a signalindicative of the thermal environment, and wherein the detecting asurface disturbance includes: determining whether the signal falls belowa first level, the first level indicative of a first type of surfacedisturbance; and determining whether the signal rises above a secondlevel, the second level indicative of a second type of surfacedisturbance.
 15. The method of claim 14, wherein the detecting aninteraction includes:determining whether, within a predetermined timeperiod, the signal oscillates, said oscillating being indicative of theinteraction between the head and the medium.
 16. A method for detectingsurface conditions of a medium moving relative to a head,comprising:monitoring a thermal environment over the moving medium;monitoring a magnetic environment on the moving medium; and processingsaid monitored thermal and magnetic environments including:(a) detectingthe presence or absence of surface disturbances encountered on themoving medium using said monitored thermal environment, and (b)detecting the presence or absence of magnetic disturbances encounteredon the moving medium using said monitored magnetic environment.
 17. Themethod of claim 16, whereinwhen no surface disturbances are detected bythe detecting step (a) in a given region of the medium and a magneticdisturbance is detected by the detecting step (b) in the given region,said processing indicates the magnetic disturbance is not caused by asurface disturbance.
 18. The method of claim 16, whereinwhen aprotrusion surface disturbance is detected by the detecting step (a) ina given region of the medium and no magnetic disturbance is detected bythe detecting step (b) in the given region, said processing indicatesthe protrusion is a particle on the moving medium.
 19. The method ofclaim 16, wherein the processing further includes:(c) detecting aninteraction between the head and the medium using the monitored thermalenvironment and the monitored magnetic environment.
 20. The method ofclaim 19, wherein the detecting steps (a) and (b) coincidentally detectprotrusion or recess surface disturbances on the moving medium.